Typically, a fuel injector comprises an armature, including a needle valve, movable between a first and second position for causing the needle valve to contact and separate from a valve seat. The extremes of these first and second positions are often defined by mechanical stops. The armature is moved in one direction by an electromagnetic force generated by a coil of wire and reciprocally moved in the opposite direction by a return spring. When the armature needle valve impacts a stop, it bounces.
In high speed fuel injectors, each bounce of the needle valve meters a small uncontrolled amount of fuel into the engine, to the detriment of emissions. As can be appreciated, the leakage of fuel into the engine will also result in very unfavorable fuel economy. At either end of its motion, the armature has kinetic energy as a result of its mass and velocity. With no means for dissipating that energy, it is returned to the armature by the elastic collision with the stop. Eventually, the energy is dissipated after a series of collisions and bounces. The bounce of the armature needle valve affects the operation of a fuel injector by prolonging or shortening the duration of injection and causing excessive wear in the valve seat area. This bouncing causes increased injection time and increased injected fuel quantity, thereby reducing the precision of fuel quantity, fuel delivery and poor atomization.
The armature needle valve of a gasoline fuel injector contributes to the control of the metering of gasoline in an automotive engine. Typically the armature needle valve assembly is manufactured of two materials that perform different functions. The first is the armature, that is made of a magnetic material such as stainless steel. When introduced into the magnetic circuit, the armature moves until it strikes the stator, thus unseating the needle valve causing the flow of fuel to begin. The second component is the needle valve which is typically made from a stainless steel material and is swaged to the armature. The needle valve has a radius ground on the tip which seats in a cone shaped valve seat, thus sealing the flow of gasoline until actuation of the magnetic circuit causes it to lift, initiating the flow of fuel. This assembly will be exercised in excess of a billion cycles during its life. The speed with which the assembly lifts is significant, as the timing of the fuel injection event is important to the timing of the engine. The speed is dependent on a number of technical parameters, one of which is the weight of the assembly. Directionally, the lighter the better.
It is seen then that there exists a need for an improved armature needle valve assembly which overcomes the problems associated with prior art armature needle valve assemblies.